1. Field of the Invention
This invention relates to manufacturing hollow, elongated bodies by means of hydrostatic extrusion, and more particularly to a method and an apparatus for use in manufacturing hollow, elongated bodies of generally rectangular cross section.
2. Description of the Prior Art
At the present time many hollow tubes of rectangular cross section are manufactured by performing the following operations: extruding a cylindrical tube; drawing that tube in a first direction; annealing that tube; drawing that tube in a second direction; and annealing that tube. The annealing processes may be eliminated or their number reduced by proper selection of reduction ratios and utilization of different materials. The aforementioned manufacturing process can have several product quality problems associated therewith. These include poor inside corner integrity which is caused by cracks and folds which are present along the inside corners of the final product and are the result of non-uniform metal distribution occurring during the multiple drawing operations required in that manufacturing process. The outside surface of the rectangular cross section tubes produced by the drawing process often has an undesirable, wavy characteristic as opposed to a desirable flat surface geometry.
A rectangularly shaped tubular product, of conductive material, is often used to provide cooling water passages in generator stator windings where it is interspersed with many other solid, current carrying conductors. Poor inside corner integrity of the cooling water passages can cause leakage and costly generator shut downs and overhauls. Non-planar side geometry of the rectangular tubes can cause difficulty in winding the stator and supplying sufficient current carrying conductors in the limited space provided for them. Therefore, formation of such conductors calls for a very reliable technique.
Hydrostatic extrusion is a recently developed metal forming technique which combines the benefits of large work piece reductions with good lubrication characteristics. Conceptually, the work piece is positioned in a high pressure chamber with its leading end situated in registry with a die. The extrusion forces are then generated by a moving ram or other pressurizing device and transmitted to the work piece through a pressure transmitting medium. Such hydrostatic extrusion can be utilized to effect a one step rectangularly shaped tube forming process which eliminates the drawing method that is associated with many of the previously mentioned product imperfections. Patents illustrating hydrostatic extrusion processes for the manufacture of symmetrically round products are U.S. Pat. No. 3,712,103 and 3,727,444.
U.S. Pat. No. 3,808,860 proposes a hydrostatic extrusion process and apparatus for producing tubular bodies including bodies having cross sections of noncylindrical shape, such as rectangular, as exemplified in its FIG. 7. The apparatus and method proposed are considered to require undesired complexity in die and billet configurations and to provide relatively poor lubrication characteristics between the die and billet which would hinder uniform billet flow and reliable final product geometry, including inside corner integrity.